Hamlet tells Horatio:
The king doth wake to-night and takes his rouse,
Keeps wassail and the swagg'ring up-springs reels...
“Wassail” implies a lot more than good health. One of the definitions in my collegiate dictionary is “A festivity characterized by much drinking.” This is what Hamlet objects to. King Claudius is a heavy drinker throughout the play. He is indulging in heavy drinking when he is attending the fencing bout between Hamlet and Laertes and is killed finally killed. No doubt Claudius is drinking heavily for at least three reasons. One is that he is celebrating the fact that he has succeeded in becoming king and marrying Gertrude. Another is that he wants to set an example to others, to encourage them to drink and be merry in order to feel good about having him as their new king. But probably the most important reason for his heavy drinking is that, like many heavy drinkers, he is trying to drown a guilty conscience in liquor. He is pretending to be happy, but inwardly he is eaten up with guilt, suspicion, and fear of divine punishment, as he clearly displays in Act 3, Scene 3 when he is trying to pray.